The book presents the major developments in modern technologies and applications of RES for over fifty years. A whole creative era is described, with Greece offering new ideas and contributing to the development of technology by successfully participating in the European and international arena towards the increased use of wind and solar energy in power generation. Included in this book are research projects and interesting missions with commentaries on the technologies and international developments related to RES, which have shown remarkable progress and development in the years that followed. Particular emphasis is placed on the energy transition, the greatest challenge of the 21st century, which will bring about a transformation in the economy and society. Renewable energy sources, mainly solar and wind energy, with their low production costs, together with energy storage and advanced management and control strategies, will be the main sources offering environmental and social benefits, while lacking the high negative effects on health and the environment. As described, the wider use of electricity becomes attractive, while the production of hydrogen for all other energy uses begins. An electricity system aiming at 100% renewable energy use is feasible and competitive against the current fossil-fuel dominated system.